Lots of people have questions about the spacing of crops in the square foot gardening system. During classes, most certified SFG instructors including me talk about the simple and general spacing of 1, 4, 9, and 16. As we explain, the big plants such as cabbage, broccoli, cauliflower, tomatoes, and kale will be planted 1 per square foot. The reason is simple. As you look at the "thin to" directions on the back of the seed package for these crops it will say "12 inches." That's were you get the spacing of 1 per square foot.
The next general spacing will say "thin to 6 inches" on the packet. These are crops such lettuce, marigolds, swiss chard, strawberries, arugula, bok choi, etc. that will be planted 4 per square. The picture above is an example. Right now these are outside under the protection of a cold-frame being hardened-off. In a few days I will plant all of these plants in one square foot. By the way, this is a magnificent lettuce variety called forellenschluss. You surely can't buy it in any grocery store an but you can easily grow it in your garden. And can I say, you will be so glad you did? The wine-red markings with the lime-green leaves make this head of lettuce look as good as it tastes.
The next spacing is "thin to 4 inches" and include crops like spinach, beets, onions, and bush beans. These are planted 9 crops per square. You might think your bush beens are crowded, and they are. But there is no wasted space in the square foot gardening system. As long as it says "thin to 4 inches," this will be the correct spacing.
Last are the crops that say "thin to 3 inches." Carrots, scallions, radishes, turnips, etc. are examples of this spacing. Sixteen carrots in one square? That's quite the use of space. If you have a traditional single row garden this will take up 4 feet in a linear row.
There are some other spacings that don't fit the 1, 4, 9, 16 spacing. These include some of the squash or melon plants. As I look at my butternut squash packet, it says "space every 24 inches." This tells me that I will use 1 squash plant per 2 square feet. If I want to have 2 squash plants to harvest I'm going to need 4 square feet to plant them in. For something like cucumbers we plant 2 per square. So, in 2 square feet we will have 4 cucumbers plants growing.
Sometimes you may come across an unusual spacing that you're not used to. For example, I have a variety of lettuce that says "thin to 12 inches." That's unusual because lettuce is normally planted 4 per square inch or every 6 inches. In this case I will simply place 2 or 3 seeds in the middle of the square and let it grow. This is obviously a very large head of lettuce that will be harvested in a short 55-60 days that breaks the general spacing guidelines.
By looking at the "thin to" information on the seed packed you will always be correct. Keep a heads up for my upcoming eBook coming out soon. I think you'll really enjoy it